Depends on the batsmen. Some of them drive away from the body, in that case you are better of bowling over the wicket, outside offstump, force them to drive loosely at a ball spinning and possibly angling in. Opens up the chance for both edges, or even bowling them through the gate.
Or if the batsman is very strong off his legs, then you bowl an outside-offstump line and wait for him to try and swing one to leg.
If the batsman plays over his pads a bit, or is more secure through the offside, then around the wicket is worth a shot. Pitch it on around middle and wait for him to make the mistake. I like this angle a lot, because if your accuracy is right then you become very hard to score off - the batsman has to either hit you against the line or against the angle.
It does also depend on how much turn you're getting and how well you're controlling your line and length on that day. If the pitch has a lot of spin in it, I'd rather bowl over the wicket and keep the ball outside off. Make them drive against the spin. Have a slip, short leg/short midwicket in place.
If it's not turning so much, but if I feel I'm bowling well, I try around the wicket. It's a naturally more defensive option though - you get your wickets from batsmen trying to score quickly of faults in their technique. So not recommended if you need wickets and the batsmen are just blocking away. Probably better off bowling over the wicket, and just a hit outside offstump them. Get them leaving one too close to them, or poking at one outside the body, or even missing one that turns in...
